Various techniques are known for producing filaments convertible into polyimide filaments from a diversity of starting materials. At present, much attention is being focused on the production of continuous monofilaments from various polymers convertible into carbon for use as a substrate material. The prior art has indicated, for example, that filaments suitable for conversion to polyimide filaments may be made by spinning an aqueous solution of an organic base salt of a polyamic acid of a diprimary diamine and a tetracarboxylic acid which is capable of forming a dianhydride into an aqueous or water miscible coagulant bath which chemically interacts with the organic base salt to regenerate the polyamide acid or otherwise convert the salt into an insoluble form. See, for example, U.S. Pat. No. 3,529,051.
It has now been found that by selecting the proper polyamic acid and wet spinning it into a preselected coagulating bath, a simple and extremely effective process for forming superior filaments of polyamic acid suitable for conversion to polyimide filaments may be produced.